1. Field of the Invention
The present invention relates to a method for the preparation of optical articles having improved abrasion resistance compared to optical articles of the prior art.
The invention also relates to a method for the preparation of abrasion resistant optical articles bearing an upper layer having hydrophobic or hydrophilic properties, leading in the latter case to antifogging articles upon an appropriate treatment.
The invention also relates to optical articles, especially ophthalmic lenses for spectacles obtained by the method of the invention.
2. Description of Related Art
Abrasion resistance of optical articles, especially ophthalmic lenses for eyeglasses, has always been an important technical problem, especially for organic lenses, whose surfaces are more prone to scratching and abrasion than inorganic lenses.
A technical solution described in the prior art is to apply a hard inorganic layer at the surface of the organic lens.
JP05173002 describes a bi-layer system: one first very thick layer (1,500 nm to 2,000 nm) obtained by evaporation of SiO under partial pressure of oxygen and, deposited thereon, a SiO2 or MgF2 layer, which is not limited in thickness but whose thickness generally ranges from 80 to 120 nm.
The first thick SiO2 layer is formed under an oxygen partial pressure, typically 2.10−4 torr (2.7×10−4 mbar) of oxygen. The partial pressure and deposition rate of this first layer are controlled in such a manner that the difference of refractive index between the optical part and the SiO reaction vapour deposition film is within +/−0.5%. According to JP05173002, the deposition of the second layer prevents reflection.
Good abrasion and adhesion resistance of the film are obtained.
The above bi-layer is directly deposited on the substrate itself (without conventional hard coating)
U.S. Pat. No. 5,597,622 relates to a process of providing a scratch resistant coating for a lens made of an organic material (such as made of CR39®). A very thin adhesion layer of SiO is applied first and is subsequently provided with a thick SiO2 layer.
The first layer has a thickness of one molecule of SiO up to 20 nm and, as said previously, is used for improving adhesion.
The first SiO layer is obtained by vaporizing SiO and irradiating the substrate and the SiO layer being formed with a plasma.
A thickness of at least 500 nm for the second layer made of SiO2 is necessary for the wearability. Indeed, U.S. Pat. No. 5,597,622 patent discloses that thinner SiO2 layers break down even if they are very hard.
Numerous patents have disclosed the use of abrasion resistant coating compositions that can be defined as hybrid layers, i.e. they have organic/inorganic properties. They are generally obtained by hydrolysis and condensation of organic alkoxysilanes, especially epoxyalkoxysilanes providing a highly cross-linked matrix.
Generally such coatings contain also a relatively high amount of inorganic fillers such as colloidal silica and/or colloidal metal oxides.
Other classically used coatings are (meth)acrylic coatings that can be organic coatings or hybrid coatings, if containing the same kind of fillers previously described.
As (meth)acrylic coatings are very hard as such, they are often used without inorganic fillers.
The usual thickness of such coatings ranges from 1 to 5 microns.
The above abrasion resistant coatings might be used in combination with anti-reflective (AR) stacks deposited thereon. These AR stacks are generally made of alternated high refractive index and low refractive index inorganic layers, deposited under vacuum (physical vapour deposition, chemical vapour deposition (CVD), optionally under plasma assistance (PECVD).
The use of an inorganic sublayer applied between a substrate bearing an abrasion resistant coating and an AR stack is known in the art.
For instance, US 2008213473 discloses the use of a SiO2 sublayer interposed between an abrasion resistant coating and an AR stack.
According to a main characteristic of the method disclosed in US2008213473, the exposed surface of the sub-layer is submitted to an ionic bombardment treatment before depositing the AR stack.
This treatment is typically conducted under vacuum, by using for example an argon ion beam generated by means of an ion gun. US2008213473 observed that such method makes it generally possible on one hand to improve the abrasion resistance properties of the whole antireflection coating and on the other to increase its adhesion properties, especially the adhesion of the multilayered stack to the sub-layer.
The sub-layer needs to be relatively thick, at least 75 nm, and its thickness generally ranges from 75 to 200 nm. US 2008213473 describes that the adhesion of the sublayer can be improved by introduction of a gas during the deposition of the sublayer, such as rare gas, oxygen or nitrogen.
The patent application WO2009004222 describes an ophthalmic lens having an AR stack deposited on a SiO2 sublayer comprising two layers wherein a first layer is deposited without ion assistance and the second layer of said sublayer is deposited with ion assistance.
The above AR stacks, apart from the inorganic sublayer (that can itself be a composite one having multiple layers) comprise at least 4 mineral layers involving different materials having different internal stresses and the mechanical properties of the AR including adhesion and abrasion resistance are the result of a subtle balance between layers that are under compressive or tensive strength.
Generally, the consequence of depositing multiple inorganic layers on an abrasion resistant coating is to fragilize the whole stack, especially if a high number of inorganic layers is deposited on an abrasion resistant coating.
There is still a need in the art to obtain coatings having high abrasion resistant properties that are simple to prepare, and that are not used in combination with antireflective coatings, especially inorganic antireflective coatings.
Numerous patents have proposed technical solutions to improve the abrasion resistant properties of abrasion resistant coating by trying to modify the intrinsic properties of such coatings, for example in case of abrasion resistant sol/gel coatings, by using precursors increasing the degree of crosslinking of the abrasion resistant coating matrix or by using specific curing catalytic systems.
A first aim of this invention is to provide an optical article, having improved abrasion resistant properties compared to the prior art.
Another aim of this invention is to provide an optical article having improved abrasion resistance starting from an optical article already coated with an abrasion resistant coating without intrinsically modifying such abrasion resistant coating.